Metallurgical furnace and method of firing the same



Feb. 29, 1944. 1-1. G. ELDER ET AL METALLURGICAL FURNACE AND METHOD OFFIRING THE SAME v 2 shts-sheet 1 Filed Oct. 29, 1940 fZDEE andliweizhifi."

F 4- H. G. ELDER EIAL 2,343,004

METALLURGICAL FURNACE AND METHOD OF FIRING THE SAME 2 Sheeis-Sheet 2Filed Oct. 29, 1940 fiwemt'ara: #48040 6 E4055 4/24 'JOH/V M0 47;

Patented Feb. 29, 1944 UNITED v STATE s YPATENT' orr cs" METALLURGICALFURNACE AND METHOD OF FIRING THE SAME Harold G. Elder, Chicago, and JohnF. Mowat,

- La Grange, 111.

Application October 29, 1940, Serial No. 363,336

6 Claims.

This invention relates to furnaces and, particularly, to an improvedmetallurgical furnace for heating ingots and the likeand to an improvedmethod of operating the same.

Various, types of furnaces, more commonly satisfactory, and in mostfurnaces the burners were so positioned therein that the flame producedthereby was in extremely closeproximlty to the ingots being heatedtherein. In such furnaces it was therefore necessary to limit the flametemperature by carefully controlling the fuel input to the burners so asto avoid overheating of the ingots and consequent melting or burning ofthe metal from which the ingots were made which was not onlyinconvenient and troublesome, but also inefficient and relativelyexpensive in their operation. Accordingly, it is one of the objects ofthe present invention to provide an improved furnace for heating ingotsand the like which is simple and inexpensive in its construction and.operation and at the same time, a furnace which uses less fuel than anyfurnace heretofore suggested or used, thereby resulting in increasedefliciency. It is another object of the invention to provide an improvedfurnace for heating ingots and the like in which the time for heatingthe ingots or articles therein has been reduced to a minimum due to theextremely high rate of heat initially supplied to the furnace.

It is a further object of this invention to pro- --vide a furnace forheating ingots and the like of an improved construction and an improvedand more economical method of firing and operating the same.

Various other objects and advantages of this invention will-,become moreapparent in the course of the following specification, and will beparticularly pointed out in the appended claims.

In the accompanying drawings there is shown, for the purpose ofillustration and description, one embodiment and a modification thereofwhich our invention may assume in practice.

In these drawings:

Figur 1 is a horizontal section through the improved metallurgicalfurnace our invention;

Figure 2 is a vertical section taken on the line II-II of Figure 1;

Figure 3 is a horizontal section similar to Figure 1 showing a furnaceor soaking pit of a slightly modified construction in accordance withour invention; and,

.Figure 4 is a vertical section taken on the line IV-IV of Figure 3. v

Referring more particularly to Figure l of the drawings, there is showna conventional type circular furnace 2 or soaking pit for heating ingotsand the like comprising a circular side wall 3,

usually made of refractory brick, so as to furnish a cylindrical-shapedheating chamber 4 therein having a flat hearth 5 arranged centrallythereof upon which the ingots 6 or articles to be heated are placed 'inspecial relation to each other as shown in Figure 1. There is arrangedin the-center of the heating chamber 4 and extending through the hearth5 a vertically arranged outlet port I for the downward removal of thewaste gases from the heating chamber. The bottom portion of the sidewalls 3 of the furnace is extended outwardly therearound as at 8 so astoprovide an annular main combustion chamber 9 between the outer ingots orarticles and the inner side of the bottom side wall portions 0 withinthe heating chamber. There isprovided a dome-shaped refractory toplllwhich is removable for the purpose of chargingthe ingot or articles tobe heated into the furnace and for removing .the same therefrom.

According to the present invention. there is suitably arranged at spacedapart intervals around the furnace in the outwardly extending bottomportion 8 of the circular side wall 3 cppositethe, main combustionchamber 9 of the heating chamber, a plurality of pairs of horizontallydisposed burners l2, namely, four pairs in the present instance, andthere is arranged between each of the pairs of burners l2 a horizonvvtally disposed single burner l3. Both'the pairs of burners l2 and thesingle burner l3 are arranged preferably in the same plane angularlyrelative to the circumference of the side wall 3 and substantiallytangential to'the' annular main combustion chamber 9v so as to',providefor substantially tangential firing thereof into the combustion chamberwhereby the gases will pass through the same in one direction withsufficient velocity to remain in the combustion-chamber for severalturns, thus diluting the burning gases with products of combustionand'increasing the or soaking pit of therewith, an enlarged opening orcombustion chamber l having the outer side wall l6 of each of themarranged substantially parallel to their respective burners H at aspaced distance from the main cumbustion chamber 9 and terminating in aside wall I! which is substantially tangent to the inner side wall ofthe heating chamber and outer side of the combustion chamber so that theheat produced by the outermost burners 14 associated with the enlargedopenings or combustion chambers I5 will be radiated inwardly by the sidewalls I6 and I1 thereof toward the center of the heating chamber so astoheat the outer, portions of the articles, as is clearly shown inFigure 1 of the drawings, with the hot gases adapted to circulate andheat those portions of the articles not directly affected or heated bysuch radiation.

The outermost burners l4 associated with each of the enlarged openingsor combustion chambers l5 are supplied preferably with a relatively hightemperature preheated air draft, preferably from 1600 F. to 2000 F. andthe innermost burner l8 of each of the pairs of bumers l2 together witheach of the single burners I3 is supplied preferably with an unheated orrela-' tively low temperature air draft, preferably 1200 F. maximum.Thus it will be seen that due to the fact that the outermost burners l4together with the enlarged combustion chambers l5 associated therewithare located a considerable distance from the ingots, a short sharp flamemay be used, and it is permissible-to provide a temperature which neednecessarily be limited only by the refractories from which the sidewalls l6 and ll of the combustion chambers l5 are made, thus permittingthe use of air pre- 7 heated from 1600 F. to 2000 F.

During the first part of the cycle, when the furnace is charged eitherwith cold ingots or,

ingots from which the-molds have been recently stripped, and whichcontain considerable residual heat, it is permissible to carry a highertemperature in the furnace than when theingots approach the rollingtemperature at which they are to be drawn, this temperature varying withthe type of steel or other material to be heated from 2200 F. topossibly 2600 F. During this part oi the cycle, all burners are used,with the high temperature air supplied to burners l4.

When the temperature of the ingots or articles to be heated rises, thefuel input to burners II and I 3 may be reduced, and the greater part ofthe heating done by means of burners l4. Under these conditions, withlittle or no heat input from burners I8 and I3, it would be impossibleto heat uniformly by convection and conduction. To overcome thisobjection, the vertical walls l6 and II are thus provided and soarranged that radiant heat will be supplied backwards'to theintermediate ingots, while the hot gases themselves circulate and heatthose portions of ingots not directly affected by such radiation.

The operation may be accomplished in several ways, either manually orautomatically, but preferably is accomplished through automatic control(not shown) as follows:

A temperature control of any known type may be inserted in the furnaceat one or more points adjacent the material being heated to maintain arate of heat input sufficient to raise the temperature within thefurnace at a regulated rate to a predetermined maximum temperature,

which temperature is then maintained until the heating cycle iscompleted, and the ingots or other articles tojbe heated are ready to bewithdrawn from the furnace. The control is arranged to regulate bothsets of fuel burners. The outermost burners H, or those associated withthe large combustion chambers will be supplied with air fromconventional recuperators or other heat exchangers at a, hightemperature,

.while the remainder of the burners, namely,

burners l3 and 18, will be supplied with air at lower temperature withthe air either being heated in an independent recuperator of a smallercapacity or taken from the high temperature recuperator at a point wherethe air has been heated to the desired lower temperature, but has notremained in the recuperator in contact with the heating elements longenough to attain the maximum temperature required for the hightemperature burners.

In operation, the control opens the fuel valves of all burners to themaximum position at the beginning of the cycle, when the furnace isrelatively cool, in order to maintain the maximum rate of heat input. Asthe temperature of the furnace rises and the ingots begin to heat up,the control, at a predetermined temperature, begins to reduce the fueladmitted to the burners l3 and I 8 using the lower temperature air. Atthe same time, the known-fuel-air ratio control, which proportions thefuel and air to all burners, reduces the air required for cumbustion inproportion to the adjusted fuel flow. Under some conditions, it may bepreferable for the temperature control to regulate the amount of air forcombustion, in which case the fuel ratio control be desirable to reduwill proportion the fuel to'the regulated amount of air. The reductionof fuel to the lower temperature burners continues to a secondpredetermined temperature, at which point the fuel may be reduced to apilot flame, of a volume only sumcient to maintain ignition. Instead ofreducing the fuel input in this manner, it may it independently of thehigher temperature, cutting oil fuel at a definite rateper unit of time,until the minimum input required by the pilot flame is reached.

During either of these operations, the high temperature burners l4continue to-operate at the maximum rate of heat input, until the furnacetemperature reaches the predetermined maximum, at which time the controlregulates the fuel input to the high temperature burners to maintain anydesired temperature until the ingots are ready to be withdrawn from thefurnace.

In Figures 3 and 4 of thedirawings, there is shown a furnace of aslightly modified construction in accordance with the present invention.In this construction the furnace is substantially square or rectangularin shape having a heating chamber 2| arranged therein with a hearth IIupon which the ingots, or articles to be heated tral portion of theheating chamber so as to heat are placed. There is arranged centrally ofthe hearth 2!, as before, an outlet port 22 for removal of the wastegases from the heating .chamber. The hearth 2| together with the ingotsor articles to be heated is arrangedso as to provide a main combustionchamber 23 therearound between the inner walls of the heating chamberand the ingots or articles therein. At each corner of the furnace thereis arranged in the side walls adjacent the bottom thereof a horizontallydisposed burner 24, similar to the outer burners l4 in the preferredconstruction, which are substantially tangent to the main combustionchamber 23 with each burner having an enlarged opening or combustionchamber 25 associated therewith in the adjacent side Wall of the furnacesimilar to the enlarged combustion chambers 9 in the furnace of thepreferred construction and communicating with the main combustionchamber 23. Each of the enlarged combustion chambers 23 has a side wall26 disposed substantially parallel to its respective burner 24 and themain combustion chamber, and which terminates in an angularly disposedside wall 21 so that the heat produced by the burners will be radiatedinwardly toward the center of the furnace-as before.

In this modified construction the burners 24 are supplied preferablywith a relatively high temperature preheated air draft as are theburners M of the preferred construction and after the furnace hasreached a predetermined maxthe outer portions of the articles adapted tobe heated. I

2. In a furnace of the class described for heating ingots and the likeincluding a substantially square heating chamber having a heartharranged in the center of the heating chamber upon which the ,articlesto be heated are placed, and a main combustion chamber arranged aroundthe furnace at the bottom of the heating chamber through which theheating gases are adapted to pass in substantially a circular path, ahorizontally disposed burner arranged at each of the corners of saidheating chamber substantially tangential to the circular path of thegases in the main combustion chamber, and an enlarged primary combustionchamber arranged directly in line with each of said burners andpositioned between the respective burners and the main combustionchamber and communicating therewith so that combustion of the gasesdirected imum temperature and it is desired to withdraw the ingots orarticles being heated from the furnace, the fuel inflow of those burnersis regu-.

lated and reduced as desired as before. In such construction it will beseen that the low temerature draft burners, such as burners I3 and I8 inthe'pleferred construction have been eliminated.

While we have shown and described one embodiment and a modificationthereof of the present invention, it will be seen that we do not wish tobe limited exactly thereto, since various other modifications may bemade without departing -furnace and the hearth at the bottom of theheating chambergsa plurality of pairs of horizontally disposed burnersarranged at spaced apart intervals in the furnace wall around the maincombustion chamber substantially tangential thereto and communicatingtherewith with the burners of each pair arranged substantially parallelto each other a single burner arranged between each of said pairs ofburners, said burners all being arranged in substantially the sameplane, and an enlargedprimary combustion chamber arranged in the wall ofthe furnace directly opposite one of the burners of each of said pairsand communicating with said main combustion chamber, each of saidenlarged combustion chambers having the side walls thereof constructedand arranged so that the heat produced from the burners associated witheach of them will be radiated inwardly thereby toward the ceninto eachof said enlarged combustion chambers is substantially completed beforethe gases enter said main combustion chamber, the outer side wall ofeach'of said enlarged combustion chambers being arranged substantiallyparallel to its respective burner and terminating in an inwardlyextending portion positioned substantially opposite the burner wherebythe heat from the burners Will be radiated inwardly thereby toward thecentral portion of the heating chamber so as to heat the outer portionsof the articles adapted to be heated therein.

3. In a furnace of the class described having side and top walls aheating chamber, a hearth arranged within said heating chamber uponwhich the articles to be heated are adapted to be placed, said heatingchamber having a substantially annular main combustion chamber arrangedtherein adiacent the bottom thereof around the hearth whereby theheating gases are adapted to pass solely in one direction insubstantiallyv a circular path through the combus tion chamber and,therearound, a plurality of burners arranged in the side walls of saidfurnace around the heatin'gtchamber, said burners adapted to directheating gases into said combustion chamber substantially tangentialthereto and to the circular path of the gases therein, .and an enlargedprimary combustion chamber arranged in the side walls of the furnacedirectly in line with some of said burners and positioned between therespective burners and the main combustion chamber and communicatingtherewith so that combustion of the-gases directed into each of saidenlarged combustion chambers is substantially completed before the gasesenter said main combustion chamber, each of said enlarged combustionchambers having a portion of the vertical side wall thereof arrangedangularly relative to the path of the heating gase issuing forth fromtheir respective burners, that a portion of the heat will beradiated inw'rdly by .the vertical side walls toward the central portion of theheating chamber.

4. In a furnace of the class described having a hearth arrangedcentrally'thereof upon which the articles to be heated are adapted to beplaced,

and a main combustion chamber arranged therearound whereby theheatinggases are adapted- -topass around the hearth in substantially acircular path, a plurality of burners arranged in the side walls of saidfurnace for directing the heat? ing gases into said main combustionchamber substantially tangential to the circular path of the gasestherein, an enlarged primary combustion chamber arranged directly inline with at least some of said burners and positioned between therespective burners and the main combustion chamber and communicatingtherewith so that combustion of the gases directed into each of saidenlarged combustion chambers is substantially completed before the gasesenter said main combustion chamber, the outer wall of each of saidenlarged combustion chambers being arranged substantially parallel toits respective burner and terminating inan angular portion arrangedsubstantially opposite the burner whereby the heat from the heatinggases issuing forth from said burners will be radiated backwardly towardthe central portion of the hearth and furnace.

5. In a furnace of the class described for heating ingots and the likeincluding, a cylindrical heating chamber having a hearth arranged in thecenter of the heating chamber upon which the articles to be heated areplaced with an outlet port arranged centrally'of the hearth throughwhich the waste gases pass out from the heating chamber, and a maincombustion chamber arranged around the furnace and the hearth at thebottom of the heating chamber, a plurality of horizontally disposedburners arranged in the furnace wall around the heatingchambersubstantially tangential thereto and communicating with the maincombustion chamber therein, a relatively small combustion chamberarranged in the wall of the furnace in line with some of said burnersand communicating with the main combustion chamber, and an enlargedprimary combustion chamber arranged in the wall of the furdirected intoeach of said enlarged combustion chambers is substantially completedbefore the gases enter said main combustion chamber, each outer sidewall thereof arranged substantially parallel to its respective burnerand terminating in an inwardly extending portion positionedsubstantially opposite the burner whereby the heat produced from theburners associated with each hearth arranged within said heating chamberupon which the articles adapted to be heated are placed with the heatinggases adapted to pass into the heating chamber and therearound insubstantially a circular path, a plurality of burners arranged in theside walls of said furnace for directing heating gases into said heatingchamber substantially tangential to the circular path of the gasestherein, a relatively small combustion chamber arranged in the wall ofthe furnace in line with some of said burners and communieating withsaid heating chamber, and an enlarged primary combustion chamberarranged in the wall of the furnace directly in line with the other ofsaid burners and positioned between the respective burners and theheating chamber and cor municating therewith so that combustion of thegases directed into each of said enlarged combustion chambers issubstantially completed before the gases enter said heating chamber, the

outer side Wall of each of said enlarged combusof said enlargedcombustion chambers having the 4 tion chambers being arrangedsubstantially parallel to its respective burner and terminating in aninwardly extending portion positioned substantially opposite the burnerwhereby the heat produced by the burners associated with the enlargedcombustion chambers will be radiated thereby inwardly toward the centralportion of the furnace so as to heat those portions of the articlesdisposed therein not heated by convection and conduction.

HAROLD G. ELDER.

JOHN F. MOWAT.

